In a manufacturing process of a semiconductor device, a photoresist pattern is formed on a semiconductor wafer, i.e., an object substrate through a photolithography process and etching is performed by using the photoresist pattern as a mask. At the time when an ultra fine pattern is formed, however, it is unavoidable that optical properties of an etching target film underlying the photoresist film and CD (critical dimension) of the photoresist pattern are varied by standing waves; reflection notching; and the diffraction and reflection light coming from an etching target film. Thus, in an effort to prevent light reflection from the etching target film, an anti-reflective coating made of a material exhibiting good light absorption property in a wavelength band of the light used in an exposure light source is interlaid between the etching target film and the photoresist film.
The anti-reflective coatings are generally classified into inorganic anti-reflective coatings and organic anti-reflective coatings, the latter being used mainly in recent years. Plasma etching that makes use of the photoresist film as a mask is employed in etching the anti-reflective coating (see, e.g., Japanese Patent Laid-open Application No 2005-26348).
To meet recent requirements for a fine processing in a photolithography technology, an ArF photoresist capable of forming pattern apertures of about 0.13 μm or less is used as an etching mask. However, the ArF photoresist shows a low plasma resistance to thereby tend to develop a problem of enlarging a CD. Therefore, in assuring a desired CD, etching property of an anti-reflective coating that is kept in direct contact with an etching target film is a critical issue.
However, it is intrinsically difficult to achieve an etching uniformity in the anti-reflective coating. Further, although there are a variety of anti-reflective coatings having different etching characteristics, there is no known process parameter that can be generally applied in controlling the variety of etching characteristics. For this reason, it is impossible to properly control an in-plane etching distribution (etching uniformity), and large variations in CD can easily develop in a later etching process of the etching target film, which cannot be easily overcome.
Meanwhile, on account of a wavelength of the light used in an exposure process, there is a limit in resolution intrinsically imposed on the photolithography technology set forth above. This usually makes it difficult to form an opening of a dimension smaller than the limit of resolution on the photoresist film. Recently, the increasing progress in miniaturization of semiconductor devices requires a CD smaller than that of the ArF photoresist film. In order to comply with this requirement, there has been proposed a method of shrinking a CD in an anti-reflective coating (see, e.g., International Publication No. 03/007357). This method employs a technique that realizes a critical dimension smaller than an initially available one by forming a deposition on an etched sidewall during an etching process of the anti-reflective coating. Examples of this method include a method of using a parallel plate type etching apparatus in an etching process to increase the intensity of a high frequency power applied to an upper electrode and a method of employing a gas prone to form a deposition, such as C4F8 gas or the like, as an etching gas.
However, the former method results in a poor etching uniformity while it is difficult to achieve a desired etching rate by employing the latter method, which leads to a reduced throughput.